Customer adjustment switch assembly

ABSTRACT

A thermal cycling switch mounted on a control panel for a surface cooking unit with calibration means attached to the switch and extending forwardly of the control panel for customer access. Abutment means in the path of movement of the extension determine the maximum adjustment that can be made by the user. The extension is disposed so as to normally be covered by the forwardly projecting control knob of the switch which must first be axially displaced some distance from the control panel for access to the extension.

United States Patent 1 Aldous CUSTOMER ADJUSTMENT SWITCH ASSEMBLY [75]Inventor: George C. Aldous, Mansfield, Ohio [73] Assignee: WestinghouseElectric Corporation,

Pittsburgh, Pa.

[22] Filed: Jan. 24, 1974 [21] Appl. No.: 436,282

[52] US. Cl 337/82, 337/57, 337/94, 337/347, 337/369 [51] Int. Cl. H0lh61/00 [58] Field of Search 337/44, 51,57, 64, 82, 337/94, 347, 369, 101

[56] References Cited UNITED STATES PATENTS 2,979,597 4/1961 Karlen337/44 X [in 3,869,688 Mar.4, 1975 Turner 337/44 X Aldous 337/101Primary Examiner-J. D. Miller Assistant Examiner-Fred E. Bell Attorney,Agent, or FirmF. A. Winans [57] ABSTRACT A thermal cycling switchmounted on a control panel for a surface cooking unit with calibrationmeans attached to the switch and extending forwardly of the controlpanel for customer access. Abutment means in the path of movement of theextension determine the maximum adjustment that can be made by the user.The extension is disposed so as to normally be covered by the forwardlyprojecting control knob of the switch which must first be axiallydisplaced some distance from the control panel for access to theextension.

9 Claims, 2 Drawing Figures CUSTOMER ADJUSTMENT SWITCH ASSEMBLYBACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to a thermal cycling switch and more particularly to such aswitch mounted on the control panel and having a forwardly projectingcalibration means for calibrating the switch, within certainpredetermined limits, by the customer.

2. Description of the Prior Art Thermal cycling switches are well knownin the prior art (see for example U.S. Pat. No. 3,634,802 of commonassignee) and are extensively used to control the energization ofsurface cooking units on a range or the like. Such switches typicallyinclude two spatially separated electrical contacts carried on movableleaf spring arms with one of the arms in intimate facing relationshipwith a bimetal extending over a substantial length of the arm. Thebimetal in turn is in intimate contact with a resistance heater. Theother contact carrying arm is moved in response to a rotatable cam,controlled by a shaft extending from the switch casing. The cam, in itsvarious positions at which the switch is on forces the contacts togetherwith varying deformation of the bimetal.

Closing the contacts, in addition to energizing the surface unit,energizes the heater in the switch which in turn causes the bimetal tobe deformed. The amount of initial deformation by the cam determines theamount of deformation required by heating the bimetal to open thecontacts, deenergizing thesurface unit and the heater, permittingbimetal to cool down whereupon the contacts again close and the cycle isrepeated.

It is noted that this switch does not respond to the temperature of thesurface unit but controls the percent of time there is power to the unitwhich in turn is correlated to a relative cooking temperature, such aslow, medium, high, etc., indicated by the manual control knob on theshaft.

These switches also typically include an ambient responsive bimetal tocompensate for variations in the ambient temperature causing variationsin the percent of on" time at the same setting. Also, a calibrationmember provided for adjusting the initial operation of the switch sothat at certain settings of the control shaft the switch maintains thesurface unit energized a predetermined percentage of time withinaccepted tolerances.

Although such switches have generally been satisfactory, it has beenfound that for various reasons, after a period of use, the switchesrequire recalibration. This is critical primarily at the lowest settingwhere, in switching from the of position to the initial on position, thesurface unit is maintained energized a greater percentage of the timethan desirable. (One accepted criteria is for the unit to just meltbutter at this lowest setting, which is accomplished when the unit isenergized about 5 percent of the time, with the permissible range being3 to 8 percent at this setting.) At any higher setting of the switch andchange in the percentage of on time can be accommodated merely byaltering the setting of the control knob; however, at the initialsetting there is no way to decrease the on time without turning the unitoff." Such a change in the operating characteristic of the switch hasresulted in customer complaint. And, although the switch is capable ofbeing corrected by a service call for recalibration by the calibrationmember, it has been found to be less expensive to simply replace theswitch rather than recalibrate it.

SUMMARY OF THE INVENTION The invention provides a thermal cycling switchof well known construction and further including a customer accessiblecalibration extension projecting forwardly through the panel mountingthe switch to be disposed in a generally unobtrusive positionsub-adjacent to the control knob of the switch. Abutment means areprovided to limit the calibration permitted the customer through thisdevice to an amount that is empirically known to accommodate at leastthe majority of switches that require recalibration.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of athermal cycling switch;

FIG. 2 is a perspective view of the switch mounted on a panel associatedwith a surface cooking unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention isassociated with a thermal cycling switch such as fully described in U.S.Pat. No. 3,634,802 which is herein incorporated for its more detaileddescription of such a switch. However, reference is made to FIG. 1 whichshows such a switch for the purpose of identification of its part. Thus,the switch 10 is enclosed in a box like casing 12 of rigid insulatingmaterial housing the switch contacts 14, 16. It is seen that theswitching contacts are, in the off position shown, in opposed facingspaced relationship as carried at the free end ofa pair of conductingarms 18, 20 cantilevered from the casing. Arm 18 is anchored as bywelding at its opposite end to a terminal 24 extending to the exteriorof the casing and includes an offset intermediate portion 22 forming acam following projection.

Arm 20 carrying contact 16 and likewise anchored at the end opposite thecontact to another terminal 26, is associated with a bimetal 28 alongits length, separated by a strip of insulating material so that when arm20 is conducting current, an energized resistance heater 27 causes thebimetal to expand in a direction to move contact 16 away from contact 14(i.e, clockwise as viewed in FIG. 1).

An ambient compensating bimetal arm 30 is also anchored to the terminal26 and extends for a short distance in generally the same direction asarm 20. The free end of arm 30 has a threaded aperture 32 therein thatreceives an adjusting screw 34 extending in the plane of movement ofboth arms 20 and 30. Access to the adjusting screw 34 is provided by anopening 36 in the sidewall of the casing.

The lead end of the adjusting screw abuts arm 20 and through itsrelative position adjust the spatial separation of contacts 14, 16 forcalibrating the switch to operate within a predetermined acceptablerange for the surface unit energization.

A manual control shaft 32 is rotatably mounted in the casing and extendsforwardly therefrom transverse to the plane of movement of contacts l4,l6 and carries a camsurface 34 in contact with the cam following portionof arm I8. Rotation of shaft 32 and thus cam 34 from its off" position,moves arm 18 to the left (as viewed in FIG. 1) closing contact 14 oncontact 16. Because of the configuration of the cam, the contacts areclosed under various degress of deformation of the arms. The amount ofdeformation set by the cam determines the amount of deformation thebimetal must assume before it can move its associated arm 20 to aposition where the contacts open. Thus, at any on setting, the contactsare closed until movement of the bimetal opens them whereupon the heateris deenergized and the bimetal cools to the contacts again becomeclosed,'resulting in the surface unit, controlled through these contactsbeing intermittently energized a certain percentage of time. The elapsedtime that the contacts remain close is thus dependent upon the settingof the cam. For the purpose of controlling a surface cooking unit, it isdesirable, at the lowest on setting, that the contacts remain closedonly about 5 percent of the time, with the percentage of closed timeincreasing gradually through the various higher settings of the controlshaft to approximately 50 to 60 percent. Any setting beyondthe 60percent will maintain the unit continuously energized as there is noneedto provide any variability between 60 to 100 percent as there is noappreciable distinction in the type of cooking by the unit over thisrange.

The switch is initially calibrated after assembly by the screw 34setting the spatial separation of the two contacts to a position whereinthe switch operates in the above parameters. However, after a period ofuse it is possible for the switch to require readjustment. It is pointedout that it is not necessary for the switch, at any of its intermediatesetting, to always provide the same amount of energized time which thatparticular setting has provided heretofore for the reason that anychange in the on time at any particular intermediate setting can becompensated for by adjusting the control knob in eitherdirection toaccommodate the change. However, at the lowest setting of the switch toan on position, where it is desirable to have the switch energized asurface unit only about 5 percent of the time, any change in the switchcharacteristics which causes the lowest setting of the switch tomaintain the burner .energized above the acceptable limit for thatsetting (8 percent being the largest percentage of energized timepermissible at the lowest setting to have the switch provide the rangeof cooking abilities desired) cannot be compensated for as turning thecontrol shaft to a lower setting turns the switch off. This type offailure is the most common user complaint of such a switch. Further, ithas been found less expensive to completely replace the switch in thefield than have a serviceman recalibrate it as the lead wires are easilyremoved and only two screws are employed in mounting the switch. This isless time consuming than recalibration through the use of the screw andthen testing the unit to determine if it is energized within the rangeof 3 to 8 percent of the time at the lowest setting.

Thus the present invention provides a means for the user to easily turnthe adjusting screw to recalibrate the switch to an acceptableoperation. Referring to both FIGS. 1 and 2, it is seen the adjustingscrew 34 of this switch has a manually accessible turning member 40engaging the screw 34 and extending outwardly through the accessaperture in the side wall of the casing. Member 40 includes a portion 42projecting forwardly in the same general direction as the control shaftso that it extends through an appropriately sized aperture 44 in thecontrol panel. The turning member 40 also includes an abutmentprojection '46 that at contacts adjacent stationary structure, such asthe side wall of the casing (also, it is obvious that the portion 42abutting the ends of the elongated aperture 44'could serve the samepurpose) to limit the permissible customer adjustment.

The screw threads and the positioning of the adjustment screw againstthe arm 20 of the commcrcial'embodiment of the above-described switchresults in changing the energization 1 percent for every l0 rotation ofthe screw. The abutment means of the present invention permit 50rotation thereby allowing a 5 percent change. Preferably, after theinitial factory calibration, the turning mechanism would be mounted onthe screw head such that the abutment portion was in one extremeposition permitting only outward axial movement of the screw to increasethe spatial separation of the contacts. Thus, should the switchsubsequently require recalibration to a lower setting, an adjustment ofup to 5 percent could be accommodated. Thus, assuming the lowest settingafter a period of use results in an on time of 10 to 13 percent which istoo high for this setting, the customer could readjust the switch towithin the 5 to 8 percent range which is then in the acceptable limits.It has been found that such ad justment would correct at least percentof the switches previously requiring replacement.

Externally on the forward side, the control shaft has a manual knob 48which carries indicia cooperating with indicia on the panel to informthe user of the relative setting of the switch in relation to the typeof cooking temperature the surface unit will have. In the preferredembodiment, the control knob has a flared base portion which extendsradially outwardly a sufficient distance to cover the extended portion42 of the manually accessible turning member 40. Thus, when anadjustment of the switch is required, the control knob can betelescopically pulled outwardly, revealing the extended portion foraccess, the correction made, and the knob (indexed to the shaft by acomplementary flat surfaces) replaced.

I claim:

1. In an electric cooking apparatus comprising a surface heating unitsupported on a counter member and including panel for supporting switchmeans associated with said unit, a thermal cycling switch enclosed in ahousing mounted on the back face of said panel having a pair of opposedrelatively movable contact carrying arms and a rotatable control shaftmounted with one end adjacent said arms and including means forcontrolling the closed position of said contacts, the opposite end ofsaid shaft extending forwardly through said panel to be manuallyaccessible for rotating said shaft between an off position and anyvarious on positions to vary the energization time of said heating unitover a predetermined range in accordance with the closed position ofsaid contacts for maintaining a relative cooking temperature identifiedby indicia associated with said position and wherein the improvementcomprises:

switch calibration means for correlating, within limits, the relativetemperature of said unit maintained at one of said positions of saidshaft to the indicia relating to said position, said calibration meanscomprising means for adjusting the initial position of one contact withrespect to the other, said adjusting means being incrementally movableand including a portion extending from adjacent one of said contactcarrying arms to exteriorly of said switch housing, and forwardlythrough said panel for manual access for moving said adjusting meansfrom the same side of said panel as the manual movement of said shaft,and abutment means for limiting the movement of said adjusting means.

2. In a thermal cycling switch for controlling the energization of asurface cooking unit, said switch housed within a casing mounted on theback face of a control panel associated with said cooking unit andincluding a manual control means extending forwardly through an aperturein said panel for setting said switch to energize said cooking unit to apreferred relative cooking range generally corresponding to indiciaassociated with said control means, said switch further including withinsaid casing a pair of opposed contact carrying arms and means foradjusting the relative spatial separation of said arms for calibratingsaid switch to respond within a preferred range of energizingcharacteristics, said last named means being accessible from exteriorlyof said casing and wherein the improvement comprises:

a manually accessible member operatively connected to said adjustingmeans and extending forwardly through an appropriately sized aperture insaid panel for turning said adjustment means from forwardly of saidpanel; and,

abutment means operatively associated with said turning means forlimiting the movement of said turning means to less than one full turn.

3. Structure according to claim 2 wherein said control means includes arotatable shaft extending from said casing forwardly of said panel and acontrol knob received by said shaft and having indicia thereoncoopcrating with indicia on said panel for indicating the relativesetting of said switch, the portion of said knob generally adjacent saidpanel having a sufficient radial dimension to normally cover saidturning means and its associated aperture in said panel.

4. Structure according to claim 3 wherein said abutment means limits themovement of said turning means so that the operational characteristicsof said switch can be altered only within a minimal range.

5. Structure according to claim 4 wherein said adjustment rangepermitted by said abutment means is sufficient to recalibrate a majorityof said switches, subsequent of the factory calibration, to within thepreviously determined acceptable operational characteristics.

6. A thermal cycling switch electrically connected to a surface cookingunit and housed Within a casing mounted on a control panel associatedwith said unit, said switch having a pair of opposed independentlymovable contact carrying arms, means for moving one of said arms to anyof various positions for closing said contacts with variable amounts ofbias and means associated with the other of said arms for opening andclosing said contacts in response to an elapsed time at either previouscondition of said contacts determined by said biasing force therebyresulting in said contacts cy clically energizing said cooking unit atany on setting with the elapsed time of energization variable inaccordance with the setting of said moving means of said one arm, saidlast named means including a rotatable shaft extending forwardly throughsaid panel and an indicia carrying knob attached to the extending endand indicating the relative setting of said switch and wherein theimprovement comprises:

a forwardly accessible switch calibration means for correlating therelative cooking temperature produced by said cyclical energization tothat indicated by said indicia, said calibration means including a screwand means for mounting said screw adjacent said other of said arms formovement in the plane of movement of said contacts, said screw havingone end contacting said last named arm to vary the normal position ofsaid arm, and the opposite end of said screw connected to a turningmember extending outwardly of said casing and forwardly through saidpanel through an appropriately sized aperture; and,

means for limiting the permissible rotation of said turning member to apredetermined amount less than one full turn.

7. Structure according to claim 6 wherein said forwardly projectingmoving member and associated apertures are normally covered by saidcontrol knob.

8. A thermal cycling switch for controlling a surface cooking unitmounted on the back of a.control panel associated with said unit, saidswitch comprising a casing housing a pair of spatially opposed movablecontact carrying arms, movable in a plane generally parallel to theplane of said psnel and a rotatable control shaft including means formoving said arms to various positions, the axis of said shaft disposedgenerally perpendicular to said plane of movability and having a portionextending forwardly through said panel for manual accessibility, saidforward portion supporting a control knob having indicia indicating therelative setting of said switch with respect to the energization of saidcooking unit; and,

means for adjusting the spatial relationship between said arms, saidadjusting means comprising and adjusting screw threadably received insupport means for axial movement of said screw in the plane ofmovability of said arms, said screw having one end abutting one of saidarms, the opposite end of said screw supporting means for turning saidscrew exteriorly of said casing, said turning means including a portionextending forwardly through said panel in a plane generallyperpendicular thereto; and,

means for limiting the rotation of said screw to less than onerevolution thereof, said limiting means comprising abutment meansdisposed in the normal path of said turning means.

9. Structure according to claim 8 wherein said turning means extendingthrough said panel is normally covered by said control knob.

1. In an electric cooking apparatus comprising a surface heating unitsupported on a counter member and including panel for supporting switchmeans associated with said unit, a thermal cycling switch enclosed in ahousing mounted on the back face of said panel having a pair of opposedrelatively movable contact carrying arms and a rotatable control shaftmounted with one end adjacent said arms and including means forcontrolling the closed position of said contacts, the opposite end ofsaid shaft extending forwardly through said panel to be manuallyaccessible for rotating said shaft between an ''''off'''' position andany various ''''on'''' positions to vary the energization time of saidheating unit over a predetermined range in accordance with the closedposition of said contacts for maintaining a relative cooking temperatureidentified by indicia associated with said position and wherein theimprovement comprises: switch calibration means for correlating, withinlimits, the relative temperature of said unit maintained at one of saidpositions of said shaft to the indicia relating to said position, saidcalibration means comprising means for adjusting the initial position ofone contact with respect to the other, said adjusting means beingincrementally movable and including a portion extending from adjacentone of said contact carrying arms to exteriorly of said switch housing,and forwardly through said panel for manual access for moving saidadjusting means from the same side of said panel as the manual movementof said shaft, and abutment means for limiting the movement of saidadjusting means.
 2. In a thermal cycling switch for controlling theenergization of a surface cooking unit, said switch housed within acasing mounted on the back face of a control panel associated with saidcooking unit and including a manual control means extending forwardlythrough an aperture in said panel for setting said switch to energizesaid cooking unit to a preferred relative cooking range generallycorresponding to indicia associated with said control means, said switchfurther including within said casing a pair of opposed contact carryingarms and means for adjusting the relative spatial separation of saidarms for calibrating said switch to respond within a preferred range ofenergizing characteristics, said last named means being accessible fromexteriorly of said casing and wherein the improvement comprises: Amanually accessible member operatively connected to said adjusting meansand extending forwardly through an appropriately sized aperture in saidpanel for turning said adjustment means from forwardly of said panel;and, abutment means operatively associated with said turning means forlimiting the movement of said turning means to less than one full turn.3. Structure according to claim 2 wherein said control means includes arotatable shaft extending from said casing forwardly of said panel and acontrol knob received by said shaft and having indicia thereoncooperating with indicia on said panel for indicating the relativesetting of said switch, the portion of said knob generally adjacent saidpanel having a sufficient radial dimension to normally cover saidturning means and its associated aperture in said panel.
 4. Structureaccording to claim 3 wherein said abutment means limits the movement ofsaid turning means so that the operational characteristics of saidswitch can be altered only within a minimal range.
 5. Structureaccording to claim 4 wherein said adjustment range permitted by saidabutment means is sufficient to recalibrate a majority of said switches,subsequent of the factory calibration, to within the previouslydetermined acceptable operational characteristics.
 6. A thermal cyclingswitch electrically connected to a surface cooking unit and housedwithin a casing mounted on a control panel associated with said unit,said switch having a pair of opposed independently movable contactcarrying arms, means for moving one of said arms to any of variouspositions for closing said contacts with variable amounts of bias andmeans associated with the other of said arms for opening and closingsaid contacts in response to an elapsed time at either previouscondition of said contacts determined by said biasing force therebyresulting in said contacts cyclically energizing said cooking unit atany ''''on'''' setting with the elapsed time of energization variable inaccordance with the setting of said moving means of said one arm, saidlast named means including a rotatable shaft extending forwardly throughsaid panel and an indicia carrying knob attached to the extending endand indicating the relative setting of said switch and wherein theimprovement comprises: a forwardly accessible switch calibration meansfor correlating the relative cooking temperature produced by saidcyclical energization to that indicated by said indicia, saidcalibration means including a screw and means for mounting said screwadjacent said other of said arms for movement in the plane of movementof said contacts, said screw having one end contacting said last namedarm to vary the normal position of said arm, and the opposite end ofsaid screw connected to a turning member extending outwardly of saidcasing and forwardly through said panel through an appropriately sizedaperture; and, means for limiting the permissible rotation of saidturning member to a predetermined amount less than one full turn. 7.Structure according to claim 6 wherein said forwardly projecting movingmember and associated apertures are normally covered by said controlknob.
 8. A thermal cycling switch for controlling a surface cooking unitmounted on the back of a control panel associated with said unit, saidswitch comprising a casing housing a pair of spatially opposed movablecontact carrying arms, movable in a plane generally parallel to theplane of said psnel and a rotatable control shaft including means formoving said arms to various positions, the axis of said shaft disposedgenerally perpendicular to said plane of movability and having a portionextending forwardly through said panel for manual accessibility, saidforward portion supporting a control knob having indicia indicating therelative setting of said switch with respect to the energization of saidcooking unit; and, means for adjusting the spatial relationship betweensaid arms, said adjusting means compRising and adjusting screwthreadably received in support means for axial movement of said screw inthe plane of movability of said arms, said screw having one end abuttingone of said arms, the opposite end of said screw supporting means forturning said screw exteriorly of said casing, said turning meansincluding a portion extending forwardly through said panel in a planegenerally perpendicular thereto; and, means for limiting the rotation ofsaid screw to less than one revolution thereof, said limiting meanscomprising abutment means disposed in the normal path of said turningmeans.
 9. Structure according to claim 8 wherein said turning meansextending through said panel is normally covered by said control knob.